The ability to measure air velocity in a duct system has been increasing in importance. Materials being transported in an industrial exhaust ventilation system, for instance, are combustible and may be highly flammable and explosible under certain conditions. One such material is combustible dust, which is finely divided solid material such as plastic, wood, or metal that presents a fire or explosion hazard when dispersed and ignited in air or any other gaseous oxidizers. These combustible dusts are frequently created as an unwanted by-product and are generally removed from production workspaces as transported material by a central ventilation system. Due to the combustible nature of these transported materials, it is often desirable and important to prevent the transported materials from settling in these ducts. This generally helps prevent or lower the risk of combustion occurring in the ventilation system. In order to achieve this, it is usually necessary to maintain minimum transport velocities for the given materials at all times and in all ducts of the ventilation system.
The recommended minimum transport velocity for different materials is available in A Manual of Recommended Practice, published by American Conference of Governmental Industrial Hygienists (ACGIH®). The National Fire Protection Association (NFPA) has also issued a number of publications relating to the prevention of industrial dust explosions. These standards and best practices are generally adopted into regulations set forth by OSHA, CAL/OSHA, and other state and federal regulatory bodies.
Currently, there is no air velocity meter on the market that will measure materials transported through a ventilation system such as combustible dust. All currently available velocity meters only work in clean air and obstruct the transported material, thereby blocking the duct system and collecting such material. To ensure that the air velocity is above the recommended and relevant standards, many have measured and recorded the air velocities throughout the entire ventilation system during installation. However, installers and manufacturers must regularly change their installation and manufacturing setup as a result of market changing conditions, including the release of new products, the increase of newer more efficient production machines, and space constraints and changes.
Additionally, re-measuring the air velocity in duct systems that are changed, redesigned, or upgraded is not always completed. As a result of these constant changes, the air velocities in some ventilation system ducts may become inadequate and may lead to settlement of material. The air velocities in other parts of the ventilation system may also become too high, causing a significant waste of energy. For example, in Industrial Ventilation Statistics, IETC 2006, written by Ales Litomisky, the measured velocities in the main ducts of 73% of ventilation systems have been shown to be outside the recommended range.
Due to fast-changing market conditions, manufacturers frequently change their manufacturing setup by utilizing an on-demand ventilation system. An on-demand ventilation system generally offers a better alternative than classic ventilation systems due to the use of sensors, gates, variable frequency drives, and control systems to adjust its system's performance. On-demand ventilation systems also save a significant amount of electricity on fan operation compared to classic systems up to 30% to 70%. By removing less air from buildings, additional significant savings in systems that use such air-conditioned systems increase. U.S. Pat. No. 7,146,677, issued on Dec. 12, 2006, to co-inventor Ales Litomisky, the same inventor of the present invention, the contents of which are expressly incorporated herein by this reference as though set forth in its entirety, discloses an energy efficient and on-demand ventilation system. U.S. Pat. No. 6,012,199, issued on Jan. 11, 2000, to co-inventor Ales Litomisky, is also hereby incorporated by this reference, as though set forth herein in its entirety.
In order to adjust and regulate the ventilation system properly, knowledge of air velocities along the length of the entire ventilation system while the system is being used is important. This task may be difficult because no air velocity meters available on the market to analyze material being transported in the air. Rather, manufacturers shut down its production and then measure the air flow velocity, volume, and static air pressure in the ducts of the ventilation system. This generally takes several hours of work, at which, during this time, the facility or factory stalls its production. Rather, the most commonly used air velocity meters are configured to work on a Pitot tube probe and are evaluated by a precise differential pressure meter. The Pitot tube generally consists of an impact tube which measures velocity pressure input installed inside a second tube of a larger diameter, which measures static air pressure input from radial sensing holes around the tip. This type of meter is an obstacle for the transported material and cannot be used during the normal use of a dust exhaust ventilation system.
Other types of air velocity meters work based on “thermal convective mass flow measurement.” These meters or probes, however, also present obstacles in the duct, leading to blockage of the material in the duct system and damage to the probes.
The third possible alternative to measure air velocity is to use meters with an ultrasonic transmitter and receiver. Ultrasonic meters, for instance, are typically used on boats or at airports to measure wind speed. An ultrasonic meter, however, is effectively useless in a duct used to ventilate dust due to the distortion of the ultrasonic signal by the dust or other transported material. Although it would be possible to measure air velocity in a duct based on the laser Doppler principle, such a system would be prohibitively expensive and would simply not be a viable option.
Accordingly, real-time measurements of air velocity that are energy efficient and inexpensive are currently unavailable. Rather, such real-time measurements pose a risk of obstruction with dust or other materials that are being transported with the air flow in the ventilation system.
Thus, what is needed is a cost effective and energy efficient system, method, and device that automatically provides numerous sampling of air velocity measurements. Preferably, this system, method, and device will measure dust and other materials being transported inside the duct system during factory production. Furthermore, because most ventilation systems service multiple work stations that may go online and/or offline at any moment, a system, method, and device that self regulates and provides automatic adjustments to the system to maintain an optimal air flow is also needed.